Illegal mix of collations (utf8_unicode_ci,IMPLICIT) and (utf8_general_ci,IMPLICIT) for operation '=

问题描述：MySQL进行字符串比较时发生错误：

SELECT a.equ_no, b.fullCode FROM equipment a, ( SELECT t.*, getEquTypeFullCode (t.equType_id) AS fullCode FROM equ_type t ) b WHERE substring(a.equ_no, 1, 5) = b.fullCode错误如下：

[Err] 1267 - Illegal mix of collations (utf8_unicode_ci,IMPLICIT) and (utf8_general_ci,IMPLICIT) for operation '='
解决方法：将比较等式一边进行字符串转换，如改为“CONVERT(b.fullCode USING utf8) COLLATE utf8_unicode_ci”

SELECT a.equ_no, b.fullCode FROM equipment a, ( SELECT t.*, getEquTypeFullCode (t.equType_id) AS fullCode FROM equ_type t ) b WHERE substring(a.equ_no, 1, 5) = CONVERT(b.fullCode USING utf8) COLLATE utf8_unicode_ci;